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A cylindrical lithium ion secondary battery, including a cylindrical can;
an electrode assembly in the cylindrical can with an electrolyte
solution; and a cap assembly sealing the cylindrical can, the cap
assembly including a positive temperature coefficient (PTC) device
connected to the electrode assembly, a cap-up connected to the PTC
device, solder between the PTC device and the cap-up, and an exterior
space without the solder on external circumferences of the PTC device and
the cap-up.

1. A cylindrical lithium ion secondary battery, comprising: a cylindrical
can; an electrode assembly in the cylindrical can with an electrolyte
solution; and a cap assembly sealing the cylindrical can, the cap
assembly including a positive temperature coefficient (PTC) device
connected to the electrode assembly, a cap-up connected to the PTC
device, solder between the PTC device and the cap-up, and an exterior
space without the solder on external circumferences of the PTC device and
the cap-up.

2. The cylindrical lithium ion secondary battery as claimed in claim 1,
wherein the exterior space has a width in a range of 0.1 mm to 1.5 mm.

3. The cylindrical lithium ion secondary battery as claimed in claim 1,
wherein the cap-up includes an exterior stepped portion protruding toward
the exterior space and contacting the PTC device.

4. The cylindrical lithium ion secondary battery as claimed in claim 3,
wherein a width of the exterior stepped portion is equal to that of the
exterior space.

5. The cylindrical lithium ion secondary battery as claimed in claim 3,
wherein the exterior stepped portion includes a plurality of stepped
portions spaced apart from each other.

6. The cylindrical lithium ion secondary battery as claimed in claim 3,
wherein the exterior stepped portion includes a plurality of serrations.

7. The cylindrical lithium ion secondary battery as claimed in claim 1,
wherein a top surface of the cap-up corresponding to the PTC device is
planar.

8. The cylindrical lithium ion secondary battery as claimed in claim 3,
wherein a top surface of the cap-up corresponding to the PTC device is
bent.

9. The cylindrical lithium ion secondary battery as claimed in claim 1,
wherein the cap assembly further includes an interior space without
solder on internal circumferences of the PTC device and the cap-up.

10. The cylindrical lithium ion secondary battery as claimed in claim 9,
wherein the cap-up includes an interior stepped portion protruding toward
the interior space and contacting the PTC device.

[0005] Lithium ion secondary batteries may exhibit, for example, a high
operating voltage and a high energy density per unit weight, and may be
used in portable electronic devices and power sources of hybrid
automobiles or electric vehicles.

SUMMARY

[0006] Embodiments may be realized by providing a cylindrical lithium ion
secondary battery, including a cylindrical can; an electrode assembly in
the cylindrical can with an electrolyte solution; and a cap assembly
sealing the cylindrical can, the cap assembly including a positive
temperature coefficient (PTC) device connected to the electrode assembly,
a cap-up connected to the PTC device, solder between the PTC device and
the cap-up, and an exterior space without the solder on external
circumferences of the PTC device and the cap-up.

[0007] The exterior space may have a width in a range of 0.1 mm to 1.5 mm.

[0008] The cap-up may include an exterior stepped portion protruding
toward the exterior space and contacting the PTC device.

[0009] A width of the exterior stepped portion may be equal to that of the
exterior space.

[0010] The exterior stepped portion may include a plurality of stepped
portions spaced apart from each other.

[0011] The exterior stepped portion may include a plurality of serrations.

[0012] A top surface of the cap-up corresponding to the PTC device may be
planar.

[0013] A top surface of the cap-up corresponding to the PTC device may be
bent.

[0014] The cap assembly may further include an interior space without
solder on internal circumferences of the PTC device and the cap-up.

[0015] The cap-up may include an interior stepped portion protruding
toward the interior space and contacting the PTC device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Features will become apparent to those of skill in the art by
describing in detail exemplary embodiments with reference to the attached
drawings in which:

[0017] FIGS. 1A, 1B and 1C illustrate a perspective view, a
cross-sectional view and an exploded perspective view of a cylindrical
lithium ion secondary battery according to an embodiment;

[0019] FIG. 3 illustrates an enlarged cross-sectional view of a
cylindrical lithium ion secondary battery according to an embodiment;

[0020] FIG. 4 illustrates an enlarged cross-sectional view of a
cylindrical lithium ion secondary battery according to an embodiment;

[0021] FIG. 5 illustrates an enlarged cross-sectional view of a
cylindrical lithium ion secondary battery according to an embodiment;

[0022] FIGS. 6A and 6B illustrate enlarged cross-sectional views of the
relationship between each of a cap-up, a positive temperature coefficient
(PTC) device and solder;

[0023] FIG. 7 illustrates an enlarged cross-sectional view of a
cylindrical lithium ion secondary battery according to an embodiment;

[0024] FIGS. 8A and 8B illustrate views of operations of a positive
temperature coefficient (PTC) device according to normal or abnormal
coating of a solder paste;

[0025] FIGS. 9A and 9B illustrate views of sealing operations according to
normal or abnormal coating of a solder paste; and

[0026] FIG. 10 illustrates a graph of resistance variations after an
exemplary lithium ion secondary battery is maintained under
constant-temperature and constant-humidity conditions.

DETAILED DESCRIPTION

[0027] Example embodiments will now be described more fully hereinafter
with reference to the accompanying drawings; however, they may be
embodied in different forms and should not be construed as limited to the
embodiments set forth herein. Rather, these embodiments are provided so
that this disclosure will be thorough and complete, and will fully convey
exemplary implementations to those skilled in the art.

[0028] In the drawings, thicknesses of layers and regions may be
exaggerated for clarity. Like numbers refer to like elements throughout.
As used herein, the term "and/or" includes any and all combinations of
one or more of the associated listed items.

[0029] The terminology used herein is for the purpose of describing
particular embodiments and is not intended to be limiting. As used
herein, singular forms are intended to include the plural forms as well,
unless the context clearly indicates otherwise. It will be further
understood that the terms "comprises," and/or "comprising," when used in
this specification, specify the presence of stated features, integers,
steps, operations, elements, and/or components, but do not preclude the
presence or addition of one or more other features, integers, steps,
operations, elements, components, and/or groups thereof.

[0030] In addition, it will be understood that when an element A is
referred to as being "connected to" an element B, the element A can be
directly connected to the element B or another element C may be present
between the elements A and B and the elements A and B may be indirectly
connected to each other.

[0031] It will be understood that, although the terms first, second, etc.,
may be used herein to describe various elements, components, regions,
and/or sections, these elements, components, regions, and/or sections
should not be limited by these terms. These terms are only used to
distinguish one element, component, region or section from another
element, component, region or section. Thus, a first element, component,
region or section discussed below could be termed a second element,
component, region or section.

[0032] The term "solder" or "solder paste" used herein may refer to a
connection member reflowed in a temperature range of about 180.degree. C.
to about 250.degree. C. to electrically connect a cap-up and a positive
temperature coefficient (PTC) device. In an example embodiment, the
connection member may be formed of, for example, a eutectic solder, such
as Sn.sub.37Pb, a high lead solder, such as Sn.sub.95Pb, or a lead-free
solder, such as SnAg, SnAu, SnCu, SnZn, SnZnBi, SnAgCu, or SnAgBi. For
example, the solder may include a tin (Sn) free connection member and
others not listed herein.

[0033] Referring to FIGS. 1A, 1B and 1C, a perspective view, a
cross-sectional view and an exploded perspective view of a cylindrical
lithium ion secondary battery according to an embodiment are illustrated.

[0034] As illustrated in FIGS. 1A to 1C, the cylindrical lithium ion
secondary battery 100 according to an embodiment may include a
cylindrical can 110, an electrode assembly 120, a center pin 130, and a
cap assembly 140.

[0035] The cylindrical can 110 may include a circular bottom portion 111
and a side portion 112 upwardly extending by a predetermined length from
the bottom portion 111. In the course of manufacturing the secondary
battery, a top portion of the cylindrical can 110 may be opened, and
during assembling of the secondary battery, the electrode assembly 120
and the center pin 130 may be inserted into the cylindrical can 110
together with an electrolyte. The cylindrical can 110 may be made of, for
example, steel, stainless steel, aluminum, or an aluminum alloy. The
cylindrical can 110 may include an inwardly recessed beading part 113
formed at a lower portion of the cap assembly 140 to help prevent the cap
assembly 140 from being deviated to the outside, and an inwardly bent
crimping part 114 formed at an upper portion of the cap assembly 140.

[0036] The electrode assembly 120 may be accommodated in the cylindrical
can 110.

[0037] The electrode assembly 120 may include a negative electrode plate
121 coated with a negative electrode active material (e.g., graphite or
carbon), a positive electrode plate 122 coated with a positive electrode
active material (e.g., a transition metal oxide, such as LiCoO.sub.2,
LiNiO.sub.2, or LiMn.sub.2O.sub.4), and a separator 123 positioned
between the negative electrode plate 121 and the positive electrode plate
122 to help prevent an electric short and allowing only movement of
lithium ions. The negative electrode plate 121, the positive electrode
plate 122 and the separator 123 may be wound up in a substantially
cylindrical shape. In an example embodiment, the negative electrode plate
121 may be made of a copper (Cu) foil, and the positive electrode plate
122 may be made of an aluminum (Al) foil, and the separator 123 may be
made of polyethylene (PE) or polypropylene (PP). A negative electrode tab
124 projected downwardly and extending with a predetermined length may be
welded to the negative electrode plate 121 and a positive electrode tab
125 projected upwardly with a predetermined length may be welded to the
positive electrode plate 122, and vice versa. In an example embodiment,
the negative electrode tab 124 may be made of nickel (Ni) and the
positive electrode tab 125 may be made of aluminum (Al).

[0038] The negative electrode tab 124 of the electrode assembly 120 may be
welded to the bottom portion 111 of the cylindrical can 110, and the
cylindrical can 110 may function as a negative electrode. In an
embodiment, the positive electrode tab 125 may be welded to the bottom
portion 111 of the cylindrical can 110, and the cylindrical can 110 may
function as a positive electrode.

[0039] A first insulating plate 126 coupled to the cylindrical can 110 and
having a first hole 126a formed at its central portion and a second hole
126b formed at its exterior side may be interposed between the electrode
assembly 120 and the bottom portion 111. The first insulating plate 126
may prevent the electrode assembly 120 from electrically contacting the
bottom portion 111 of the cylindrical can 110. For example, the first
insulating plate 126 may prevent the positive electrode plate 122 of the
electrode assembly 120 from electrically contacting the bottom portion
111. A large amount of gas may be generated, for example, due to an
abnormality in the secondary battery, and the first hole 126a may allow
the gas to rapidly move upwardly through the center pin 130, and the
second hole 126b may allow the negative electrode tab 124 to pass through
the same to be welded to the bottom portion 111.

[0040] A second insulating plate 127 coupled to the cylindrical can 110
and having a first hole 127a formed at its central portion and a
plurality of second holes 127b formed at its exterior side may be
interposed between the electrode assembly 120 and the bottom portion 111.
The second insulating plate 127 may prevent the electrode assembly 120
from electrically contacting the cap assembly 140. For example, the
second insulating plate 127 may prevent the negative electrode plate 121
of the electrode assembly 120 from electrically contacting the cap
assembly 140. A large amount of gas may be generated, for example, due to
an abnormality in the secondary battery, and the first hole 127a may
allow the gas to rapidly move to the cap assembly 140, and the second
holes 127b may allow the positive electrode tab 125 to pass through the
same to be welded to the cap assembly 140. In an electrolyte injection
process, the second holes 127b may allow the electrolyte to rapidly flow
into the electrode assembly 120.

[0041] Diameters of the first holes 126a and 127a of the first and second
insulating plates 126 and 127 may be smaller than a diameter of the
center pin 130, and it may be possible to prevent the center pin 130 from
electrically contacting the bottom portion 111 of the cylindrical can 110
or the cap assembly 140, for example, due to an external shock.

[0042] The center pin 130 may be in the shape of a hollow cylindrical pipe
and may be coupled to a substantially central portion of the electrode
assembly 120. The center pin 130 may be made of, for example, steel,
stainless steel, aluminum, an aluminum alloy, or polybutylene
terephthalate. The center pin 130 may prevent the electrode assembly 120
from being deformed during charging or discharging of the secondary
battery, and may serve as a path of gas movement. In some cases, the
center pin 130 may not be provided.

[0043] The cap assembly 140 may include a cap-up 141 having a plurality of
through-holes 141e, a positive temperature coefficient (PTC) device 142
installed under the cap-up 141, a safety plate 144 formed under the PTC
device 142, an insulating plate 145 installed under the safety plate 144,
a cap-down 146 installed under the safety plate 144 and the insulating
plate 145 and having first and second through-holes 146a and 146b, a
sub-plate 147 fixed on a bottom surface of the cap-down 146 and
electrically connected to the positive electrode tab 125, and an
insulation gasket 148 insulating the cap-up 141, the safety plate 144,
the insulating plate 145, the cap-down 146 and a side portion 111 of the
cylindrical can 110.

[0044] The insulation gasket 148 may be compressed between the beading
part 113 formed on the side portion 111 of the cylindrical can 110 and
the crimping part 114. The through-holes 141e, 146a, and 146b formed in
the cap-up 141 and the cap-down 146 may discharge internal gas to the
outside when an internal pressure of the cylindrical can 110 increases,
for example, due to an abnormality in the secondary battery. The internal
pressure may make the safety plate 144 upwardly reversed and electrically
separated from the sub-plate 147. Then, the safety plate 144 may be
ruptured and the internal gas may be discharged to the outside.

[0045] The cap-up 141 and the PTC device 142 may be electrically connected
to each other by the solder 143. Resistance of the PTC device 142 may be
increased according to an increase in the temperature, the PTC device 142
may prevent current or over-current from flowing, and the secondary
battery may be kept in a stable state. The relationship between each of
the cap-up 141, the PTC device 142 and the solder 143 will later be
described in more detail.

[0046] An electrolyte (not shown) may be injected into the cylindrical can
110 and may allow movement of lithium ions generated by an
electrochemical reaction in the negative electrode plate 121 and the
positive electrode plate 122 during charging and discharging of the
battery. The electrolyte may be a non-aqueous organic electrolyte
including a mixture of a lithium salt and high-purity organic solvent.
The electrolyte may be, for example, a polymer using, e.g., including, a
solid electrolyte.

[0047] Referring to FIG. 2, an enlarged cross-sectional view of a region 2
of FIG. 1B is illustrated.

[0048] As illustrated in FIG. 2, the cap assembly 140 may include the PTC
device 142 electrically connected to the electrode assembly 120, and the
cap-up 141 electrically connected to the PTC device 142. The cap assembly
140 may further include the solder 143 coated between the PTC device 142
and the cap-up 141 and reflowed to then be cured. The PTC device 142 and
the cap-up 141 may be electrically connected to each other by the solder
143. The safety plate 144 and the cap-down 146 may further be provided
between the PTC device 142 and the electrode assembly 120. The safety
plate 144 may be electrically connected to a bottom portion of the PTC
device 142, the cap-down 146 and the sub-plate 147 may be electrically
connected to the safety plate 144, the positive electrode tab 125 may be
electrically connected to the sub-plate 147, and the positive electrode
tab 125 may be electrically connected to the electrode assembly 120.

[0049] The PTC device 142 may include a device portion 142a, a top
conductive pattern 142b formed on a top surface of the device portion
142a, and a bottom conductive pattern 142c formed on a bottom surface of
the device portion 142a. As described above, the resistance may be
increased when the temperature of the secondary battery rises, and the
PTC device 142 may prevent charge or discharge current from flowing.

[0050] An exterior space 141a without the solder 143 formed along external
circumferences of the cap-up 141 and the PTC device 142 may further be
provided. The exterior space 141a having a hollow interior inwardly
extending a predetermined length or width from the external
circumferences of the cap-up 141 and the PTC device 142 may further be
formed.

[0051] A horizontal length of the exterior space 141a may be in a range of
about 0.1 mm to about 1.5 mm. If the horizontal length of the exterior
space 141a is smaller than about 0.1 mm, the solder 143 may flow, e.g.,
flow up, to the external circumferences of the cap-up 141 and the PTC
device 142 during a reflow process, the cap-up 141 may be directly
short-circuited to an unwanted region of the PTC device 142 and/or the
safety plate 144, and current or over-current may be prevented from being
cut off. If the horizontal length of the exterior space 141a is greater
than about 1.5 mm, the external circumference of the cap-up 141 may be
bent during a crimping process, and internal sealing efficiency of the
secondary battery may be lowered.

[0052] An interior space 141b without the solder 143 formed along internal
circumferences of the cap-up 141 and the PTC device 142 may further be
provided. The interior space 141b having a hollow interior outwardly
extending a predetermined length from the internal circumferences of the
cap-up 141 and the PTC device 142 may further be formed.

[0053] The predetermined length of the interior space 141b may be in a
range of about 0.1 mm to about 0.4 mm. If the length of the interior
space 141b is smaller than about 0.1 mm, the solder 143 may flow up to
the internal circumferences of the cap-up 141 and the PTC device 142
during a reflow process, the cap-up 141 may be directly short-circuited
to an unwanted region of the PTC device 142 and/or the safety plate 144,
and current or over-current may be prevented from being cut off. If the
length of the interior space 141b is greater than about 0.4 mm, an
electrically connected region between the cap-up 141 and the PTC device
142 may be reduced, and electrical resistance may be increased.

[0054] Even if the width of the interior space 141b is smaller than about
0.1 mm, the solder 143 may mainly flow toward the cap-up 141 during a
reflow process. Wettability of the solder 143 with respect to the cap-up
141 may be higher than that of the solder 143 with respect to the PTC
device 142 (for example, the device portion 142a), and the solder 143 may
mainly flow toward the cap-up 141, rather than toward the PTC device 142,
during the reflow process. Therefore, even if the width of the interior
space 141b is smaller than about 0.1 mm, the solder 143 may rarely flow
up to an unwanted region of the PTC device 142 and/or the safety plate
144.

[0055] As described above, the solder or solder paste 143 may be coated
between the cap-up 141 and the PTC device 142m followed by reflowing, and
the cap-up 141 and the PTC device 142 may be integrally formed. The
electrolyte and moisture may not penetrate into a portion between the
cap-up 141 and the PTC device 142, an oxidation layer may not be
generated, and resistance of the cap assembly 140 may be prevented from
increasing.

[0056] A coating area and/or a coating amount of the solder or solder
paste 143 may be optimized, and the solder or solder paste 143 may
prevent direct short-circuits from being generated between the cap-up 141
and an unwanted region of the PTC device 142 (for example, the bottom
conductive pattern 142c) and/or the cap-up 141 and the safety plate 144,
and component cracks and/or sealing failures, for example, due to
bending, may be suppressed during a crimping process.

[0057] As described above, the solder or solder paste 143 may be coated on
the cap-up 141 or the PTC device 142. That is, by way of example and not
limitation, in an embodiment, the solder or solder paste 143 may be
pre-plated on the cap-up 141 or the PTC device 142.

[0058] Referring to FIG. 3, an enlarged cross-sectional view of a
cylindrical lithium ion secondary battery according to an embodiment is
illustrated.

[0059] As illustrated in FIG. 3, the cap-up 141 may further include an
exterior stepped portion 141c protruding toward the exterior space 141a
and making contact with the PTC device 142. The exterior stepped portion
141c protruding toward the exterior space 141a may protrude toward the
PTC device 142 by a predetermined length from the external circumference
of the cap-up 141.

[0060] A horizontal length or width of the exterior stepped portion 141c
may be equal to that of the exterior space 141a. In an example
embodiment, the length of the exterior stepped portion 141c may be in a
range of about 0.1 mm to about 1.5 mm. The length of the exterior stepped
portion 141c may be smaller than about 0.1 mm or may be greater than
about 1.5 mm.

[0061] A thickness of the exterior stepped portion 141c may be equal to
that of the solder 143. In an example embodiment, the thicknesses of the
exterior stepped portion 141c and the solder 143 may be in a range of
about 0.01 mm to about 0.03 mm.

[0062] The exterior stepped portion 141c may prevent the solder 143 from
flowing to the external circumferences of the cap-up 141 and the PTC
device 142 during reflowing.

[0063] The exterior stepped portion 141c of the cap-up 141 may be directly
electrically connected to the top conductive pattern 142b of the PTC
device 142.

[0064] As described above, the exterior stepped portion 141c may be
further formed on a region corresponding to the exterior space 141a, and
the solder 143 may not flow to the external circumferences of the cap-up
141 and the PTC device 142 during reflowing (for example, the exterior
stepped portion 141c may serve as a dam for preventing the solder 143
from flowing out during reflowing). Accordingly, an electric
short-circuit may be prevented from occurring between the cap-up 141 and
an unwanted region of the PTC device 142 (for example, the bottom
conductive pattern 142c) and/or between the cap-up 141 and the safety
plate 144. The solder 143 and the exterior stepped portion 141c may
maintain the cap-up 141 at a perfectly or substantially planar state
during a crimping process, and component cracks and/or sealing failures,
for example, due to bending, may be suppressed from occurring.

[0065] The exterior stepped portion 141c may be formed on the top
conductive pattern 142b of the PTC device 142, rather than on the cap-up
141. The region corresponding to the exterior space 141a may be plated
for a relatively long time during a plating process for forming the top
conductive pattern 142b, and the exterior stepped portion 141c may be
formed relatively thickly on the region corresponding to the exterior
space 141a to extend from the top conductive pattern 142b to the cap-up
141. The exterior stepped portion 141c may make close contact with the
cap-up 141. The effects exerted by the exterior stepped portion 141c
upwardly protruding from the top conductive pattern 142b of the PTC
device 142 may be the same as described above.

[0066] Referring to FIG. 4, an enlarged cross-sectional view of a
cylindrical lithium ion secondary battery according to an embodiment is
illustrated.

[0067] As illustrated in FIG. 4, the exterior stepped portion 241c formed
in the cap-up 141 may include a plurality of exterior stepped portions.
In an example embodiment, the exterior stepped portion 241c may be in the
shape of, e.g., include, a plurality of serrations, e.g., protrusions.
For example, the exterior stepped portion 241c may be in the shape of an
inverted triangle having a width gradually decreasing toward the PTC
device 142.

[0068] As described above, the plurality of exterior stepped portions 241c
may be formed on the region corresponding to the exterior space 141a, the
solder 143 may not flow to the external circumferences of the cap-up 141
and the PTC device 142 during reflowing, and an electric short-circuit
may be prevented. The solder 143 and the exterior stepped portion 241c
may maintain the cap-up 141 at, e.g., in, a planar state during a
crimping process, and component cracks and/or sealing failure, for
example, due to bending, may be suppressed from occurring.

[0069] The stepped portions 141c and 241c of the cap-up 141 may be formed
by a metal processing process, such as, for example, casting, forging,
rolling, or punching.

[0070] Referring to FIG. 5, an enlarged cross-sectional view of a
cylindrical lithium ion secondary battery according to an embodiment is
illustrated.

[0071] As illustrated in FIG. 5, a top surface of the cap-up 141
corresponding to the PTC device 142 may be substantially bent. For the
purpose of forming an exterior stepped portion 341c, the cap-up 141
corresponding to the exterior space 141a may be bent by a predetermined
angle, and the top surface of the cap-up 141 corresponding to the
exterior stepped portion 341c may be positioned to be lower than the top
surface of the cap-up 141 corresponding to the solder 143. A region of
the cap-up 141, corresponding to a boundary between the exterior stepped
portion 341c and the solder 143, may be defined as a bent portion 341b.

[0072] The exterior stepped portion 341c may still make direct contact
with the top conductive pattern 142b of the PTC device 142, and the
solder 143 may be prevented from flowing during reflowing.

[0073] The exterior stepped portion 341c and/or the bent portion 341b of
the cap-up 141 may be formed by a metal processing proves, such as, for
example, pressing.

[0074] As described above, the exterior stepped portion 341c and/or the
bent portion 341b of the cap-up 141 may be provided in the cap-up 141,
and component cracks and/or sealing failures, for example, due to
generation of an oxidation layer, an increase in the resistance, a short
circuit, or bending, may be suppressed.

[0075] Unlike in the embodiment shown in FIG. 5, in the embodiment shown
in FIGS. 2 to 4, the top surface of the cap-up 141 corresponding to the
PTC device 142 may be perfectly or substantially planar.

[0076] Referring to FIGS. 6A and 6B, enlarged cross-sectional views of the
relationship between each of a cap-up (141), a positive temperature
coefficient (PTC) device (142) and solder (143) are illustrated.

[0077] As illustrated in FIG. 6A, a length (width) of the exterior space
141a may be denoted by L and a thickness of the solder 143 may be denoted
by D. As described above, the thickness of the solder 143, i.e., D, may
be in a range of about 0.01 mm to about 0.03 mm.

[0078] The following Example and Comparative Example are provided in order
to highlight characteristics of one or more embodiments, but it will be
understood that the Example and Comparative Example are not to be
construed as limiting the scope of the embodiments, nor is the
Comparative Example to be construed as being outside the scope of the
embodiments. Further, it will be understood that the embodiments are not
limited to the particular details described in the Example and
Comparative Example.

[0079] As listed in Table 1, to form the exterior space 141a having a
length equal to L, the solder or solder paste 143 was coated on the
cap-up 141 or/and the PTC device 142, followed by reflowing, and
component resistance failures and crimping failures were investigated.

[0080] The component resistance failure refers to the solder 143 flowing
up to external circumferences of the cap-up 141 and the PTC device 142
during reflowing, to make the solder 143 directly short-circuited to an
unwanted region of the PTC device 142 (for example, a bottom conductive
pattern) or/and the safety plate 144.

[0081] The crimping failure refers to the cap-up 141 and/or the PTC device
142 being bent while crimping a can and an insulation gasket and the
interior of the secondary battery not being sealed.

[0082] As listed in Table 1, when the length L of the exterior space 141a
was in a range of about 0 mm to about 0.1 mm, component resistance
failures (for example, short failures) were generated in 28 among 200
samples.

[0083] When the length L of the exterior space 141a was in a range of
about 1.5 mm to about 1.6 mm, crimping failures (for example, sealing
failures) were generated in 10 among 40 samples.

[0084] Therefore, an appropriate length (width) L of the exterior space
141a may be in a range of about 0.1 mm to about 1.5 mm.

[0085] As illustrated in FIG. 6B, when the exterior stepped portion 141c
is formed on the region corresponding to the exterior space 141a, a
probability of generating component resistance failures and crimping
failures may be further lowered.

[0086] If the length L of the exterior space 141a is smaller than 0.1 mm,
existence of the exterior stepped portion 141c may prevent component
resistance failures from being generated, unlike in the embodiment
illustrated in FIG. 6A in which component resistance failures may be
generated. If the length L of the exterior space 141a is greater than 1.5
mm, existence of the exterior stepped portion 141c may prevent crimping
failures from being generated, unlike in the embodiment illustrated in
FIG. 6A in which crimping failures may be generated.

[0088] When an exterior stepped portion was used, no component resistance
failure was generated among 100 samples and no crimping failure was
generated among 20 samples. When an exterior stepped portion was not
used, 21 component resistance failures were generated among 100 samples
and 4 crimping failure were generated among 20 samples.

[0089] Referring to FIG. 7, an enlarged cross-sectional view of a
cylindrical lithium ion secondary battery according to an embodiment is
illustrated.

[0090] As illustrated in FIG. 7, an interior stepped portion 141d may
further be formed along internal circumferences of the cap-up 141 and the
PTC device 142. The cap-up 141 may further include the interior stepped
portion 141d protruding toward the PTC device 142 and making contact with
the PTC device 142.

[0091] As described above, the interior stepped portion 141d may prevent
the solder 143 from flowing up to interior circumferences of the cap-up
141 and the PTC device 142 during reflowing, and component cracks and/or
sealing failures, for example, due to generation of an oxidation layer,
an increase in the resistance, a short circuit, or bending, may be
suppressed from occurring.

[0092] Referring to FIGS. 8A and 8B, operations of a positive temperature
coefficient (PTC) device according to normal or abnormal coating of a
solder are illustrated.

[0093] As illustrated in FIG. 8A, when the cap-up 141 includes the
exterior stepped portion 141c and the solder 143 is normally coated and
reflowed, the PTC device 142 may be tripped when the temperature of the
secondary battery rises, and current or over-current may be cut off.

[0094] As illustrated in FIG. 8B, when the cap-up 141 does not include the
exterior stepped portion 141c and the solder 143 is not normally coated
and reflowed (for example, when there is no exterior space), the solder
143 may make the top conductive pattern 142b and the bottom conductive
pattern 142c of the PTC device 142 directly short-circuited, the PTC
device 142 may be prevented from being tripped when the temperature of
the secondary battery rises, and current or over-current may be prevented
from being cut off. When the temperature of the secondary battery rises,
the current or over-current may flow to the cap-up 141 while by-passing
the PTC device 142, and the secondary battery may become unstable.

[0095] Referring to FIGS. 9A and 9B, sealing operations according to
normal or abnormal coating of a solder paste are illustrated.

[0096] As illustrated in FIG. 9A, when the cap-up 141 includes the
exterior stepped portion 141c and the solder 143 is normally coated and
reflowed, each component may maintain a good degree of planarity during
crimping, and excellent sealing efficiency of the secondary battery may
be achieved.

[0097] As illustrated in FIG. 9B, when the cap-up 141 does not include the
exterior stepped portion 141c and an excessively large exterior space is
provided, the planarity of each component may not be maintained during
crimping, and the sealing efficiency of the secondary battery may be
lowered.

[0098] Referring to FIG. 10, resistance variations after an exemplary
lithium ion secondary battery is maintained under constant-temperature
and constant-humidity conditions are illustrated.

[0099] The X-axis indicates the number of days during which an integrated
assembly of the cap-up 141 and the PTC device 142 was left undisturbed,
and the Y-axis indicates resistance values of the integrated assembly of
the cap-up 141 and the PTC device 142. The integrated assembly of the
cap-up 141 and the PTC device 142 was left undisturbed under the
conditions of 60.degree. C. in temperature and 95% in humidity.

[0100] In the Example, an integrated assembly of the cap-up 141 and the
PTC device 142 was used, the cap-up 141 having an exterior space 141a
having a length in a range of 0.1 mm to 1.5 mm. In the Comparative
Example, a separate type assembly of a cap-up and a PTC device (without
solder) was used. Results are summarized in Table 3.

[0101] As shown in FIG. 10 and Table 3, after being maintained under
constant-temperature and constant-humidity conditions, the secondary
battery according to Example had superior resistance variations to the
secondary battery according to the Comparative Example. In the
Comparative Example, the resistance variation of the secondary battery
increased as the time in which it was left undisturbed increased. In the
Example, the resistance variation of the secondary battery was saturated
to a predetermined value without being further increased.

[0102] By way of summation and review, a lithium ion secondary battery may
be classified as, for example, a cylindrical secondary battery, a
prismatic secondary battery, or a pouch type secondary battery. For
example, a cylindrical lithium ion secondary battery may include a
cylindrical electrode assembly, a cylindrical can coupled to the
electrode assembly, an electrolyte injected into the can to allow
movement of lithium ions, and a cap assembly coupled to one side of the
can to prevent leakage of the electrolyte and separation of the electrode
assembly.

[0103] Provided is a cylindrical lithium ion secondary battery, which may
optimize a coating area and/or a coating amount of a solder or solder
paste between a cap-up and a positive temperature coefficient (PTC)
device constituting a cap assembly, and component cracks and/or sealing
failure, for example, due to generation of an oxidation layer, an
increase in the resistance, a short circuit, or bending, may be
suppressed.

[0104] Also provided is a cylindrical lithium ion secondary battery, which
may include a stepped portion and/or a bent portion formed in a cap-up,
and component cracks and/or sealing failure, for example, due to
generation of an oxidation layer, an increase in the resistance, a short
circuit, or bending, may be suppressed.

[0105] Example embodiments have been disclosed herein, and although
specific terms are employed, they are used and are to be interpreted in a
generic and descriptive sense only and not for purpose of limitation. In
some instances, as would be apparent to one of skill in the art as of the
filing of the present application, features, characteristics, and/or
elements described in connection with a particular embodiment may be used
singly or in combination with features, characteristics, and/or elements
described in connection with other embodiments unless otherwise
specifically indicated. Accordingly, it will be understood by those of
skill in the art that various changes in form and details may be made
without departing from the spirit and scope of the present invention as
set forth in the following claims.